Increased Bandwidth: Use EtherChannel and combine two or four links into one logical link. It will double or quadruple your bandwidth. For example, four 100Mb Fast Ethernet connections bonded into one could provide you up to 800Mb/second, full-duplex.

Provides Redundancy: Since there are many Ethernet links combined into one logical channel, it automatically allows more available links in case one or more links go down.

Load Balance Traffic: EtherChannel balances the traffic load across the links, thereby increasing efficiency on your networks.

                      

The figure above shows some of the key components of an EtherChannel bundle between SW1 and SW2, with their Gi1/0/1 and Gi1/0/2 interfaces.

The physical links can be aggregated into a logical link called an EtherChannel bundle or a bonded interface

802.3ad mode is an IEEE standard also called LACP (Link Aggregation Control Protocol). It includes automatic configuration of the aggregates, so minimal configuration of the switch is needed. This standard also mandates that frames will be delivered in order and connections should not see misordering of packets. The standard also mandates that all devices in the aggregate must operate at the same speed and duplex mode.

Balance-RR: If this mode is set, packets are transmitted in sequential order from the first available slave to the last. Balance-RR is the only mode that will send packets across multiple interfaces that belong to the same TCP/IP connection. When utilizing multiple sending and multiple receiving links, packets are often received out of order, which results in segment retransmission, for other protocols such as UDP it is not a problem if client software can tolerate out-of-order packets.

Active-backup: This mode uses only one active slave to transmit packets. The additional slave only becomes active if the primary slave fails. The MAC address of the bonding interface is presented onto the active port to avoid confusing the switch. Active-backup is the best choice in high availability setups with multiple switches that are interconnected.

Balance-XOR: This mode balances outgoing traffic across the active ports based on the hashed protocol header information and accepts incoming traffic from any active port. Mode is very similar to LACP except that it is not standardized and works with layer-3-and-4 hash policy.

Balance-tTLB: This mode balances outgoing traffic by peer. Each link can be a different speed and duplex mode and no specific switch configuration is required as for the other modes. The downside of this mode is that only MII link monitoring is supported (ARP link monitoring is ignored when configured) and incoming traffic is not balanced. Incoming traffic will use the link that is configured as "primary".